Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 AM EDT Thu May 02 2019 Valid 12Z Sun May 05 2019 - 12Z Thu May 09 2019 ...Weather Highlights/Threats... A lead low will lift offshore Sunday into Monday to produce an area of enhanced rains over the northern mid-Atlantic and Southern New England. A trailing front back across the Southeast, the Gulf and the southern Plains will meanwhile remain a focus for local heavy rain/thunderstorms. Well upstream, upper ridging will remain anchored over the northeastern Pacific which will keep drive split flow over the Lower 48 next week. An unsettling and initially closed southern stream low will work into California and the Southwest as a series of cooling and precipitation focusing northern stream systems skirt along the US/Canadian border. Expect scattered showers and some convection into the Great Basin/Rockies. Precipitation (generally rain with high snow levels) will mostly focus on higher elevations, but some valley rain. Moisture influx into the region appears to be modest. This pattern will also favor periods of organized strong convection with a cell training/excessive rainfall/runoff threat as a series of hard to time northern and southern stream impulses eject over the east-central U.S. overtop a building upper ridge over the Deep South. Systems may be primed to periodically tap deepening moisture and instability pooled by return Gulf of Mexico inflow into two surface frontal systems/enhanced baroclinic zones. ...Guidance/Predictability Assessment... The WPC medium range product suite was composed from a blend of compatable GFS/ECMWF/UKMET/Canadian model guidance Sunday. Opted to transition to an ensemble mean based forecast starting Monday amid growing forecast spread and uncertainty, primarily with smaller scale impulse timing/interactions and convection genesis. This maintains good WPC continuity. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml